Positron Emission Tomography (PET) is a metabolic imaging modality used to diagnose, stage, and restage seven Medicare-reimbursed cancer types. Currently ninty-six US cyclotrons proton-bombard stable enriched O-18 water, producing F-18 fluoride ion to synthesize F-18 fluorodeoxyglucose (FDG) used in 350,000 PET scans per year. Our goal is to significantly lower the cost of FDG and thereby lower the cost of PET scans by about 10%. CTI, EBCO, GE, and IBA cyclotrons (10-20 MeV) are capable of twice the beam power that can be dissipated by their targets. We seek to demonstrate feasibility of our thermosyphon target invention that may have the potential to double F-18 production and fully realize cyclotron potential. The thermosyphon beam and condenser volumes are loaded full of target water, sealed at the top, and run with beam while pressurized at the bottom with 30 atm He. This results in a heat transfer geometry much superior to conventional targets, which load partially and seal at the bottom, leaving a reflux void to be pressurized at the top. The thermosyphon self-regulates, moving liquid (displaced by thermal expansion and condenser steam) in and out the bottom port. The condenser steam space is in proportion to the beam power until beam strike liquid is invaded at the upper power limit. Foreign gas molecules impeding vapor transport are avoided. Aim 1 is demonstrating reliability of a new production thermosyphon target by running at Duke University Medical Center, four days a week for one month to support FDG synthesis for clinical PET and PET/CT scanning of 15-20 patients/day (beams at or above 30 microamps and F-18 yields at or above 70% theoretical). Duke F-18 production is predicted to improve from the current 600 mCi/hr to 2000 mCi/hr with the new thermosyphon target. Aim 2 is designing beta-test targets for cyclotrons capable of long runs at 1.0-1.5 kW beam power, namely a CS-15 (15 MeV, 10mm beam) at Anchorage, AK, and a domestic GE PETrace (16 MeV, 15mm beam). Aim 3 is fabrication and initial beam testing of beta-test targets at the two sites. Collaborators will cost-share fabrication, retaining possession in exchange for sharing operating experience and publication authorship. Phase II experiments will lead to a commercial product by measuring F-18 yields up to the power limit, and optimizing target depth and condenser geometry to minimize 0-18 water use.